With the rapid development of the Internet and web technology, governments worldwide have caught onto this revolution and shown rapid development of electronic government (e-government) in the public sector. Nowadays, there are a significant number of e-governments that are accessible via the Internet and provide a range of information and services. However, existing research indicates that e-government still faces the challenge of generating greater users’ interaction in terms of accessing information, utilizing services and participating in e-government decision making. Among a variety of reasons for this challenge, usability and credibility have been found to be the key factors in users’ decisions about e-government engagement and need to be explored. This research attempts to evaluate the usability and credibility of current e-governments, focusing on specific e-government websites in the UK. This research adopted heuristic evaluation, which is based on users’ perception, to implement a thorough and in-depth assessment of e-government websites. In addition, to obtain a more comprehensive evaluation, users’ performance was measured in order to reveal the level of users’ interaction with e-government websites when they perform a set of practical tasks. The research design was a quasi-experimental, consisting of two linked experiments. Experiment 1 aimed to evaluate usability and credibility of the target e-government websites, identifying a range of existing usability and credibility problems. Based on the usability and credibility problems found, design solutions were proposed for each of the target e-government websites. Experiment 2 aimed to examine the effects of the proposed design solutions on the usability and credibility problems identified on the redesigned e-government websites. The findings of experiment 1 suggested that the e-government websites need to improve their usability and credibility. In particular, the most serious usability problems found in the target e-government websites lay within the areas of “aesthetic and minimalist design”, “recognition rather than recall”, and “consistency and standards”. In addition, the most serious credibility problems identified were within the areas of “site looks professional”, “make site easy to use and useful”, and “show the honest and trustworthy people behind the site”. The findings of experiment 2 revealed that the usability and credibility problems found in experiment 1 had been improved by the proposed design solutions. Furthermore, these improvements might increase the overall usability and credibility of the target e-government websites, making the users’ task performance better within the redesigned e-government websites. Based on the findings of the experiments, this research developed a set of usability and credibility guidelines. Each guideline addressed a number of the specific usability and credibility elements at the detailed level of e-government website design. These guidelines can be helpful to guide designers to develop more usable and credible e-government websites.